1. Field of the Invention
This invention relates to a method and apparatus for speech signal detection in speech analysis and for decision and classification as to whether the detected speech signal is voiced or unvoiced. More particularly, this invention relates to a method and apparatus which are suitable for reliably executing the detection and classification without dependence upon the level of a speech input.
2. Description of the Prior Art
The most fundamental step of processing in speech analysis for the purpose of speech synthesis or recognition includes detection of a speech signal and decision and classification as to whether the detected speech signal is voiced or unvoiced. Unless this processing step is accurately and reliably done, the quality of synthesized speech will be degraded or the error rate of speech recognition will increase.
Generally, for the detection and classification of a speech signal, the intensity of a speech input (the mean energy in each of the analyzing frames) is the most important and decisive factor. However, use of the absolute value of the intensity of the speech input is undesirable because the result is dependent upon the input condition. In the prior art off-line analysis (for example, analysis for speech synthesis), such a problem has been dealt with by the use of the intensity normalized by the maximum value of the mean energy in individual frames of a long speech period (for example, the total speech period of a single word). However, such a manner of analysis has been defective in that it cannot deal with the requirement for real-time speech synthesis or recognition.